In a hydraulic excavator as a construction machinery, a boom and an arm, as well as an arm and a bucket, are swingably coupled by a pin.
In a portion coupled by the pin, namely in a pin hinge joint, lubricant oil such as grease is generally injected into between the pin and a boss to make the swinging motion smooth, as well as to prevent wear and noise caused by metal contact.
Further, a bearing seal called radial lip seal is used to prevent earth and the like from entering through between the pin and the boss from an outside, as well as to prevent the lubricant oil from leaking out through a clearance between the pin and the boss.
An example of such a bearing seal is described in, for example, Patent Document 1.
The bearing seal as described in Patent Document 1 includes, as shown in FIG. 14, a flex ring 1, a tension ring 2, and a seal ring 3. The flex ring 1 fits to a boss 4, and the seal ring 3 is attached so as to be brought into contact with a pin 5.
In the bearing seal mentioned above, a mounting ring 6 is mounted on an outer periphery of the flex ring 1 to make the flex ring 1 easy to be fitted to the boss 4.
In the bearing seal as described in Patent Document 1, when mounting the seal ring 3 to the pin 5, the tension ring 2 is expanded in a radial direction so that a diameter thereof is enlarged, and the seal ring 3 is brought into press contact with the pin 5 by a fastening force caused by shrinkage of the tension ring 2. Thus, a large surface pressure (namely, seal surface pressure) in the radial direction, for example, a surface pressure of 20 N/cm is generated on the seal ring 3.
For this reason, a material having high tensile modulus of, for example, 300 to 14,000 MPa and high elongation of, for example, 5% or higher is used for the tension ring 2.
As described above, since the seal surface pressure on the seal ring 3 is generated by the fastening force of the tension ring 2, the seal ring 3 is required to be provided with two seal lips of a seal lip 3a and a stabilizer lip 3b to improve sealing performance.
If the seal lip is formed of only one piece, the tension ring 2 does not evenly shrink in a width direction (axial direction of pin 5), and fall of the seal lip occurs, so that the seal lip is not properly brought into press contact with the pin 5, thus causing the sealing performance to be deteriorated. For this reason, the aforementioned stabilizer lip 3b is added, whereby the tension ring 2 can evenly shrink in the width direction, and the seal lip can be properly brought into press contact with the pin 5. Accordingly, sealing performance in normal time can be favorably maintained.
Since the seal ring 3 has the seal lip 3a and the stabilizer lip 3b, when the pin 5 and the boss 4 rotate against each other, a frictional force is generated in two positions, that is, the seal lip 3a and the stabilizer lip 3b, so that the frictional force becomes greater.
The flex ring 1 is made strong to resist the great frictional force. In other words, as the frictional force becomes greater, when the pin 5 and the boss 4 rotate against each other, a great rotating force acts on the flex ring 1. Accordingly, the flex ring 1 may be damaged if it is weak, therefore, as described above, the flex ring 1 is made strong so as not to be damaged.
[Patent Document 1] JP-A-06-201056